Because of some bad input, a Template Haskell function is generating broken code. How can I apply -ddump-splices to just one file in Yesod?
I know that fixing the bad input is the solution, but debugging that depends on what is being generated by Template Haskell, which I can't see in the error output from what I normally run
stack exec -- yesod devel
I think that the function staticFiles in src/Settings/StaticFiles.hs must be a Template Haskell function. I thought I would give a look into what is generated by that, but I realized I am out of my depth, naively trying stack exec --ghc-options='-ddump-splices' -- yesod devel to no effect.
How can I apply -ddump-splices to just one file in Yesod?
Other higher-level comments on debugging Yesod/Template Haskell are much welcomed.
You can add a pragma to the Haskell file, where you want to render the splices. Like:
{-# OPTIONS_GHC -ddump-splices #-}
{-# LANGUAGE TemplateHaskell #-}
import SomeModule(someTHFunction)
foo = $(someTHFunction 14 25)
When I test this locally, it will only dump slices of template Haskell in the file where this pragma is added, so you can add it to the files where you are interested in the template Haskell implementation, and leave out the other ones.
Related
Does Crystal expose its internal parser as a standard library as python does with it's ast module? How to parse crystal source code and get the AST of it?
Yes! In fact it ships the entire compiler in the stdlib. So we can just access the parser to get an AST:
require "compiler/crystal/syntax/*"
root = Crystal::Parser.new(%(
class Foo
def hello
:world
end
end)).parse
The official docs do not include the Crystal::ASTNode and its subclasses, the ones you find the docs are the ones exposed the macro language and thus slightly differ. So you'll have to dive into the source code to see how to make use of the AST.
Why are there clj and cljs folders in my lein re-frame template as below? And why do they both include files called .core that appear to use the same namespaces? I've been told this is the place to start when learning re-frame, but I cannot find any explanations of why the templates are setup the way they are or created including the content they include.
There is no explanation for any of the boilerplate or code that comes with any lein template which make them very hard to use for beginners.
Thanks in advance.
This setup is used to separate Clojure Backend code from the ClojureScript frontend. It isn't actually necessary and I don't particularly recommend it but I can explain its history and why you'd want to do it.
For the ClojureScript side it really doesn't matter at all.
When builing a Clojure Backend you will often deploy in some "uberjar" or "uberwar" setup. This means that all source files and dependencies are packed into one single .jar file (basically just a zip file). This is typically done by including all files from a specified set of directories, so it would include src/clj but not src/cljs. If everything is in one directory it would add the .cljs files as well although they are never used by the Clojure backend. So in essence it just makes your "uberjar" bigger. It is not an important optimizations but some people prefer to keep things lean and clean.
In addition some developers just prefer to separate the code this way. In this case the template authors did.
One answer:
As the comments point out, some projects develop the backend code (Clojure) and the frontend code (ClojureScript) in the same project repo. I think this is a mistake as it can easily lead to confusion and entanglement (esp. if using lein to start both projects simultaneously). IMHO it is better to keep both front- and back-end parts in separate repositories. I would also strongly recommend using figwheel-main and the Clojure deps build tool for the CLJS code.
Another answer:
For CLJS code, any macros have to be defined in an "earlier" compilation stage. Thus, for namespaces defining macros, you often see files like either util.clj or util.cljc to define the macro, and then a file like util.cljs where the macro is used.
You can find more information below, but it is subtle & confusing:
https://clojurescript.org/guides/ns-forms
https://clojurescript.org/about/differences
https://blog.fikesfarm.com/posts/2018-08-12-two-file-clojurescript-namespace-pattern.html
Apologies in advance for the somewhat discursive nature of this clump of related questions; I hope the answers will be a useful resource for newcomers to Clojure.
I have just begun to learn Clojure, motivated in part by this essay. I'm not a professional developer but I have several decades of programming experience (ARexx, VB/VBScript/VBA, then Perl and daily use of R starting in 2011). My platform is Windows 7 64-bit. I'm using Emacs 24.3, cider 20131221 and Leiningen 2.3.3 on Java 1.7.0_45 Java Hotspot 64-bit server. I have bought Clojure Programming and the Clojure Data Analysis Cookbook and dipped into both. I have found them promising but I am getting lost in the detail.
Obviously the thing to do is to get stuck in and experiment with code exercises and small tasks, but the immediate problem for me has been the complexity of structuring, organising and even just plain running projects in Clojure. With R I can get away with a file of plain text containing the bulk of the code, perhaps with one or two others containing common functions for larger projects.
Clojure is very different and with no experience in Java I am struggling to put the pieces together. Clojure Programming has a whole chapter on organising and building projects, but it is so comprehensive that conversely I'm finding it difficult to tease out the information relevant to me now. I guess I'm looking for something like this answer on Swank, but the tools seem to have moved on since then. So here goes.
Leiningen produces amongst other things a project.clj file that contains the project definition and dependencies. I think I get this. Can I use this file for code not related to the definition, below the defproject, or is it best to leave this untouched and have the code itself in different clj file(s)?
If the answer is to leave the project.clj file alone, how is the relationship between that and other files established? Is it simply that all the clj files in the project folder are counted part of the project?
How do I define the main code file, the 'entry point' of the project? Let's say I have project.clj and main.clj with some helper functions in common.clj - how are the relations between these three files defined? I can call functions from main.clj but how does the project know that main is the core of the project if/when I package the project into an uberjar?
If I have a number of clj files, what is the best way to import functions? I have read about require and use (and import and refer and...) but I don't fully understand the difference and those two keywords are difficult to search for. The examples for REPL in the Clojure Data Analysis Cookbook most often opt for use. I found a similar question but it was a little over my head.
This is more tool-specific, but as Emacs seems to be widely used it seems fair to ask: what's a good workflow to run small bits of code given (say) the main.clj example given above? Currently I just open the main.clj file in Emacs, do an M-x cider-jack-in to establish the REPL, experiment in the REPL, then when I want to try something I select the whole buffer and select Eval region from the CIDER menu (C-c C-R). Is this standard operating procedure or utterly misguided?
Is there a convention for defining namespaces? I think I understand that namespaces can cover multiple clj files and that ns is used to define the namespace. Should I explicitly define the namespace (at the beginning of) every file of code? Clojure Programming has some recommendations but I'm interested in input from other users.
Clojure programming says to "Use underscores in filenames when namespaces contain dashes. Very simply, if your namespace is to be com.my-project.foo, the source code for that namespace should be in a file located at com/my_project/foo.clj". (EDIT as explained in this useful answer and also this one). This restriction would never have occured to me. Are there any other gotchas with regard to naming namespaces and variables? R frequently uses dots in variable names but I guess given the Java connection that dots should generally be avoided?
No, don't put actual code in there unless you know what you are doing (e. g. generate the version number for defproject from the local git repository like in the repositories of juxt)
The project.clj is simply one big parameter to Clojures build tool leiningen. See an example here https://github.com/technomancy/leiningen/blob/master/sample.project.clj. For example, you could specifiy a different source directory than src in the :source-path.
Default is the -main function in project.core, but you can specify various different configurations in the project.clj.
require is preferred. :use imports all publics of a namespace unless you use it in conjunction with :only. Require let's you use an alias for an entire namespace with :as, but you can have the same effect from use with :only using :refer. Notice that in ClojureScript :use without :only is not even allowed.
This is normal. There are other combos like e.g. C-c C-k to reload the entire file of the buffer. If you find yourself entering too many forms into a REPL and would rather edit them in a separate buffer https://www.refheap.com/22235.
I like to experiment trying to name namespaces in in verbs rather than nouns, e. g. I prefer myproject.parse, myproject.interpret, over myproject.parser, myproject.interpreter etc. But that's a question of personal style. EDIT: Yes, explicitly define the naming of the namespace by its filename and the ns form at the beginning of the source file. It is unusual to have multiple source-file defining one namespace.
Afaic this is the only caveat regarding naming of namespace. You can hardly know it in advance.
I like your "worried" approach. You will (hopefully) find out that Clojure and especially Leiningen are almost nonsense-free in terms of these questions.
Regarding REPL use: I saw your comment under #Mars answer that you want to use a REPL in a fashion that you can re-use what you are entering. Two things:
Dynamic development is awesome, allowing you to test small components or functions interactively without the need to run an entire program written for that purpose.
If you find your self entering huge forms at the REPL that you intend to de-/recompose into functions or tests later, I recommend editing them in a seperate clj file that is not part of the project source (i. e. not in a namespace). You can then use this Emacs hack to eval forms from a Clojure buffer in the REPL. Ideally split your Emacs in two windows (C-x 3) with the nrepl buffer on one side and your .clj on the other side. Then use C-x C-. from within the clj file to have the form at point pasted into the nrepl and be evaluated. Installation instructions are at the link (and your .emacs file usually resides in the home directory).
#Igrapenthin's answers are great. Here are a few other thoughts.
On namespaces, this tutorial is great.
Just to clarify re #2: No, don't just put the .clj files anywhere under the project. They have to be under src/, or in whatever directories are listed (as strings) in the vector after :source-paths in project.clj, if that entry exists. Then strip off that initial path when you're making your namespace names. This drove me crazy until I figured it out. (People who know better, please correct me if something here isn't right.)
One #3, you need Igraphenthin's answer, but why not just start by evaluating expressions in the REPL? I've been working on a project on and off for weeks, and it does a lot, but my -main function still doesn't do anything. I just run whatever parts I'm working on. Well, you're used to languages with fully operational prompts--you decide.
EDIT: Whether or not you define the -main function to do anything, you can also put :use or :require keywords in the ns statement that defines the namespace for that same file. These will automatically get invoked when you start the REPL with lein repl, and so whatever you have made available through the ns keywords will be available at the REPL. That way, you have your previous work available, but you can play around with it in different ways in the REPL. (Also, if you don't like the default name for the file that's automatically loaded, you can redefine it in project.clj with :main. Igraphenthin alluded to that.)
Is there any plugin for VIM that I can use to index an C++ project code base?
I would apreciate functionalities like being capable of specifing a class and and may be a method and see what file/line the method/class is defined.
Regarding code navigation (and completion),
I'd take a look at clang_indexer (and clang_complete) --
ctag understanding of C++ code is quite bad, but universal-ctags has greatly improved the situation ; cscope understanding of C++ is non-existent.
Regarding plugins for C++ coding,
I have a suite for C and C++ programming. It is mainly oriented toward C++ programming, however a few, and unique features can be used in C as well:
context sensitive snippets (they require other plugins I'm maintaining);
a way to jump to a function definition from its declaration (or create it on the fly if it doesn't exists yet) (it used to requires the plugin alternate, which is a must have, however that I've forked it for my own needs) -> :GOTOIMPL;
a little tool that lists functions with a declaration and no definition, or functions with a definition and no declaration (NB: I haven't used it against C static function yet) (it requires ctags).
:Override that searches for overridable functions
:DOX that analyses C++ function signature to generate the appropriate (customizable) doxygen comment (with \param, \throw, ...)
a mapping to include the header file where the symbol under the cursor is defined* (which requires an up-to-date ctags base)
and few other things
Otherwise, I also use:
plugins like project/local_vimrc in order to have project specific settings ;
searchInRuntime to open/jump to files without the need to browse the directories of the current project ;
a refactoring plugin (that still lacks a few things ...) ;
a wrapper around :make in order to do background compiling, and to filter &makeprg results (e.g. pathnames conversions between cygwin posix form and dos form ; application of STLfilt ; etc.) (-> BuildToolWrapper which is stable, but still in an alpha stage) ;
and a few other things which have already been mentioned (alternate, ctags, ...).
Other Plugins.
Other people use c.vim, other templating systems (snipmate & co), pyclewn (that I highly recommend for debugging (with gdb) from within vim), other bracket-surrounding-and-expansion systems, ...
PS: I've answered, slightly differently, a question on the same subject on quora.
cscope is a nice tool for browsing. There is nice tutorial here.
ctags is another nice tool, I use it in my projects. Tutorial here. If you are in Ubuntu, you can install ctags by doing:
apt-get install exuberant-ctags
gtags is another tool.
I use taglist extensively.
The "Tag List" plugin is a source code browser for the Vim editor. It provides an overview of the structure of source code files and allows you to efficiently browse through source code files in different programming languages. It is the top-rated and most-downloaded plugin for the Vim editor.
Is there a library for Python that will allow me to parse c++ code?
For example, let's say I want to parse some c++ code and find the names of all classes and their member functions/variables.
I can think of a few ways to hack it together using regular expressions, but if there is an existing library it would be more helpful.
In the past I've used for such purposes gccxml (a C++ parser that emits easily-parseable XML) -- I hacked up my own Python interfaces to it, but now there's a pygccxml which should package that up nicely for you.
Parsing C++ accurately is light-years from something you can do with a regular expression.
You need a full C++ parser, and they're pretty hard to build. I've been involved in building one over several years, and track who is doing it; I don't know of any being attempted in Python.
The one I work on is DMS C++ Front End.
It provides not only parsing, but full name and type resolution. After parsing, you can basically extract detailed information about the code at whatever level of detail you like, including arbittary details about function content.
You might consider using GCCXML, which does contain a parser, and will produce, I believe, the names of all classes, functions, and top-level variables. GCCXML won't give you any information about what's inside a function.
This is a little outside your question's scope perhaps... but depending on what you're trying to achieve, perhaps Exuberant Ctags is worth looking at.
Have not tried, but using the Python bindings from LLVM's Clang parser may work; see here.
How about pyparsing?